I found the You Don't Know JS series books by Kyle Simpson very helpful.

The last one is for ES6.

https://github.com/getify/You-Dont-Know-JS

I found it helpful to go through the airbnb style guide. They have lots of examples of the "bad" (often old) way to write something, along with the "good" (often new) way. Then I updated one of my projects to follow those guidelines.

I've found Pony Foo's articles to be excellent:

https://ponyfoo.com/articles/tagged/es6-in-depth

This is a very nice and comprehensive overview:

ES6 (very comprehensive!) http://es6-features.org/#Constants

ES7 (succint, easy to read) https://h3manth.com/new/blog/2015/es7-features/

http://www.react.express is intended as a learning resource for those used to ES5 Javascript. Granted, it's for learning React through modern Javascript, so it may not be exactly what you're looking for, but it has interactive sections for new ES6 and ES7 features.

I took a class on ES6 and curated it in a github repo: https://github.com/JacobWylie/ES6

If applicable there are examples of both before and after conventions as well as links to more technical external resources.

exploringjs.com